Allylmalonyl-CoA is a short-chain, methyl-branched fatty acyl-CoA that is the S-isobutyryl derivative of coenzyme A. It has a role as a human metabolite and a mouse metabolite. It is a short-chain fatty acyl-CoA and a methyl-branched fatty acyl-CoA. The allylmalonyl-coenzyme A (AM-CoA) biosynthetic pathway has recently been almost elucidated, and it is mediated by four tcs genes (tcsA, tcsB, tcsC, and tcsD), which is unique to the FK506 biosynthetic gene cluster. The ketoacylsynthase TcsB, the propionyl-acylated, catalyzes the condensation of the propyl moiety with malonate loaded on TcsA, which comprises an acyltransferase and an acyl carrier protein (ACP) domain. The resulting β-ketopentyl-ACPTcsA gives rise to the trans-2-pentenyl-ACPTcsA through the action of endogenous fatty acid synthase (FAS) system.